Binocular observation instrument



Dec. 8, 1953 J. w. FRENCH BINOCULAR OBSERVATION INSTRUMENT 5Sheets-Sheet 1 Filed Aug. 15, 1947 m A. 4 Is ,A

YQW m w By v Dec. 8, 1953 J. w. FRENCH BINOCULAR OBSERVATION INSTRUMENTFiled Aug. 15; 1947 5 Sheets-Sheet 2 IwvnZ o/ 77 W 567m 5 Dec. s, 1953J. w. FRENCH 2,661,6 7

BINOCULAR OBSERVATION INSTRUMENT Filed Aug. 15, 1947 5 Sheets-Sheet 3Ff; :JEzmes l l/ HencZL Dec. 8, 1953 J. w. FRENCH BINOCULAR OBSERVATIONINSTRUMENT 5 Sheets-Sheet 4 Filed Aug. 15, 1947 m W. QM W W [V w mm Km,

FIG 31f. y W1 i J. W. FRENCH BINOCULAR OBSERVATION INSTRUMENT Dec. 8,1953 5 Sheets-Sheet 5 Filed Aug. 15, 1947 Jun . IHWQWZLOP T752777 Q5fien'cz. 5y 2 Ami.

Patented Dec. 8, 1953 UNITED STATES ATENT OFFICE BINOCULAR OBSERVATIONINSTRUMENT James Weir French, Glasgow, Scotland, assignor to Barr &Stroud, Limited, Glasgow, Scotland,

a British company Application August 15, 1947, Serial No. 768,722 Claimspriority, application Great Britain September 25, 1946 8 Claims.

experiment, shows the effect of reducing the objective area of one limbof a binocular, having in the other limb an objective of 3 square inchesconstant daylight aperture.

Provided the two eyes of the observer are reasonably equal, it isimmaterial which limb, either right or left, of the binocular isreduced. Experiment shows that in the case of a normal observer thedifferences are negligible, but for comfort in thecase of a hand heldbinocular the larger and heavier limb might with advantage be the righthand one.

Table 1 Objectiifre Objective R d t f Area rea 0 e no lOlIl o LargeSmall Total Apparent ggzzg Definition Contrast Limb, Limb, Illuminationpercent percent A 100 59 Very slight Unaltered... Improved B... 100 26Less than do do Improved. O 100 7 Less than10% do do Do. D 100 1. 7 Lessthan do Same as Line (1.... Slightlg worse than E 100 zero About 15%Impaircd Impaired Impaired.

lumination by the brain is increased to the extent of about ten orfifteen per cent. Binoculars hitherto have been constructed with bothlimbs of the same optical size and in general identical, apart frombeing sometimes right and left handed, as in the case .of prismbinoculars.

In accordance with the present invention we provide a binocularobservation instrument of the type in which the images from the twolimbs of the instrument, formed on the two retinas of the observer, arecombined in the brain to form a single image, characterised by thedaylight aperture of one binocular limb being substantially smaller thanthat of the other.

As a result of the invention, one limb of the binocular can be madeoptically as large as may be necessary to provide the desiredillumination and optical qualities, while the optical size of the otherlimb can be reduced substantially without proportional reduction to anyimportant extent of apparent illumination, without loss of stereoscopiceffect, and in some cases with improved definition and contrast; andfurther, the daylight aperture of one objective can be increased, andtherefore the illumination, beyond what is possible in, for example, aGalilean binocular.

Table 1, compiled from the results of a typical Table 1 shows a set ofsuch readings taken with a binocular having an objective of 3 squareinches daylight area represented in column 1 of the table, as The otherlimb of the objective was progressively reduced in area from 100% to 59%then 26%, 7%, 1.7% and finally zero, as indicated in column 2. Reductionto 59%, line A, produced only a very slight reduction of the totalapparent illumination. Stereoscopic effect, column 4, remainedunaltered. Definition, column 5, was slightly improved. i No change ofcontrast, column 6, was observable.

When the units were reduced to 26 line C, there was a small apparentreduction of total illumination, less than 5%. Stereoscopic effect wasunaltered. Both definition and contrast were improved.

A further reduction to 71%, line C, resulted in a reduction of the totalapparent illumination by less than 10%. Stereoscopic effect wasunaltered. There was a slight further improvement in definition andcontrast.

Reduction of the objective area to 1.7 caused a total reduction ofapparent illumination of less than 15%. Stereoscopic efiect was stillunaltered. The definition was as in line C. Contrast was slightly lessthan in line C.

When the objective area was reduced .to zero,

3 line E, the illumination was not reduced by more than 15% as comparedwith the total illumination when both objectives were of full 4reference to the accompanying drawings, whose figures illustrate asfollows:

Figure 1, the dioptric system of a terrestrial describe thisinvention,by way'of example, with aperture. The stereoscopic effect was imtypeglass.

paired owing to the elimination of the stereo- 6 Figure 2, the dioptricsystem of a Galilean glass scopic base.- Any residual stereoscopicappearwith the eye centrally placed.

ance may be" attributed to judgement other than Figur .3,- the samediopt ic system with the eye real stereoscopic effect. Both thedefinition and displaced.

the contrast were impaired as compared with the Figure 4, the obliquerays of Figure 2. binocular having full aperture in both objectives. 10Figure 5, the oblique rays of a Galilean system These results indicatethat inthe use of awith-reduced'objective and same angular field asbinocular having full aperture in both objectives, Figured; as comparedwith a monocular of. the same ob- Figure 6;- a terrestrial system havinga reduced jective aperture, the brain appreciates about objectiveand thesame angular field as the more light. When the area of one objective is15 Galilean system, Figure 4. progressively decreased, there is acirogressiveloss Figured, the'largest size of Galilean objectives ofillumination within the limit of 15%. This obtainable forth'e averageinterocular distance. apparent binocular increase of illumination ex-Figure 8, the greatly increased diameter obplains the appearance ofmovement towards'the je'ctiveof one limb in comparison with reducedobserver and increased size of a target under 0bdiameter of theother,.the interocular distance servation when a sudden change. is madefrom being as in Figured; monocular vision to binocular. The greaterFigure 9,.a binocular having one Galilean limb illumination at oncecreates-the impression of large-and the other Galilean limb'small.greater nearness and size. The true stereoscopic Figure 10, a binocularhaving. one large Galie efiect is notlost so long as suflicientdirection of leanlimb and another small objective limb-comboth eyes isprovided. prising a terrestrialsystem of lenses.

The data indicated'in Table 1 were obtained Fig, 11, a binocular withone large Galilean under normal daylight conditions. Similar relimb andasmall prismatic telescope limb. suits-were, however, obtained over alarge range Figure 12, the eyepieceviewoi Figure 11. of light intensity.To illustrate this feature, Figure 13, a binocular having both limbs ofthe neutral filters which transmitted only 6% of the prismatic type, onelarge. and the-other small. incident light were placedover bothobjectives. In thecase'of an optical system having'a field Thereafterthe area of one of the objectives was viewed by an eyepiece, reductionof the objective progressively diminished in steps by theamountsdiameter does not reduce the angular field of obindicated in Table 12servation as will'b'erseen from Figure 1, which Table 2? ObjectiveObjective Reduction @23 ,gggggg, ggggg Definition coma i IlluminationA... 100- 59 Veryslightloss. Unaltered... Slightlyimproved.. Slightlyimproved. B 100 26 Slight loss do Improved Improved. C. 100 7 Less than5%.. do Asinline B As in line B. D; 100 1.7 Less than 10% do; ..do Do.E. 100 zero .do Impaired". Impaired Impaired.

The results for such very dulllight'. condition, represents the"limiting rays: of a central and indicated in Table 2, are very similarto those of oblique-beam of light entering the objective I, 2; Table 1.There. was no apparent loss of light whose optical" centre is 3.Marginal rays of the until the'illumination of one limb. had beenre'parallel beam converge" to the centre 4 of the ducedto about 59%.Stereoscopic vision wasunfield-5, 6, whence they proceed to the eyelensI, afiect'ed. There'was initially animprovement' in B; andemergeparallelalong the directions 9, I0 definition. and contrast whichcontinued unand H, I2. The obliqueray3; Sdetermines the changed tillnear the end. At. 1.7 and: zero semi-angular field of the system.aperture the loss approached 10%. It would ap- It is customary in suchinstruments toprovide pear,.therefore, thatcomparedwith the monocu- 60only half, or' even'less, light at the side of the larzin failing light,the binocular'appearsto give held. In any radial plane the limiting raysI", about 10% more illumination. Sand 3; 5, to themargini-of'thediaphragm 5, 6,

Itwill beevident'from these two tables that a therefore determine theamount ofillumination large reduction of one object glass may beeffected that'will be apparent at thelfield margin. These with advantageand without any serious lossof two rayspassto'the eyelens'LB'in thedirections total illumination. As is'customary the magni- 5, Tand'5; l3an'd'em'erge from the eyelens as fyingipower of thetwo limbs shouldbe'the same parallel rays in the directions I, M and l3, l5. andfalsoitheangular fields orotherwise the super- Thecentral oblique ray 3', 1,after-"passing through position of the darkr'imof the smaller field uponthe system, intersects. theaxis at the point IS the illuminated marginof the other is disturbing which i's'term'ed the positionof the exitpupil tothe observer. l1, 18. The eye placed at this position receivesHaving now described-the general optical printhe wholeof the lightfromtheiobjective entering ciplesiof the two main types ofbinocularscomparailel to theaxisand'thewhole of the oblique monlycalledGalilean and prismatic, we'shallnow 5 light, in this casecorresponding with half of the objective area-.-

angular field is determined by the obliquity of the line 3, 5, that itis not decreased by reduction of the objective, and that it can only beincreased by enlargement of the diaphragm 5, 6. A displacement of theeye in the plane of the exit pupil i7, 68 cuts oii light from thecentral beam and in one direction in the half light arrangementindicated also from the oblique beam.

In the particular arrangement, Figure 1, a prism system for the erectionof the image is not indicated as it does not affect the field providedthe prisms are sufliciently large.

In the case of a Galilean type of glass, as represented in Figures 2 and3, the conditions are quite diiferent. A Galilean glass comprises apositive objective and a negative eyelens. There can be no positivefield diaphragm such as l, 8 of Figure 1, the objective field 1iesbeyond the eyelens, not between it and the objective. It is then themargin of the objective that determines the field which, however, doesnot appear distinct as it is not in the focus of the eyepiece as is thecase with the field diaphragm of the binocular, Figure 1.

In Figure 2, I, 2, 3 represents the objective; 1, 8 the negativeeyelens. Rays I, I and 2, 8 of the axial beam of light that is enteringparallel to the axis pass to the eye in the parallel directions '1, 9and 8, H. For illumination of 50% at the edge of the field the limitingoblique rays are 3, 5 and 2, 6. These rays pass outwards in the paralleldirections 5, M and 6, l5. There is no exit pupil position as in thecase of Figure 1.

If, however, the eye is placed at the position It,

beam without any translation of the head.

If the head were translated sideways, as explained in connection withFigure 1, there would be cutting oiT of some light but the movement ofthe eye would enable a larger angular field at one side to be observed,as indicated in Figure 3, Where the iris I1, I 3 has been displacedsufficient- 1y to cut oil half the central beam. The limiting obliqueray is now 3, 20 and is of larger angular value than 3, l of Figure 2.There has been an increase of angular field at the expense of centralillumination and oblique illumination at one side. The eyelens 28, 2!must necessarily be increased to suit the wider beam.

In a, Galilean glass the angular field is determined by the aperture ofthe objective, and if movement of the head is permissible, to someextent by the size of the eyelens. If one objective of a Galilean glassis reduced in diameter, the angular field of the particular limb is alsoreduced. The brain, therefore, perceives an illuminated areacorresponding with the angular field of the larger limb and superposedupon it a similar area corresponding, however, with the reduced field ofthe smaller objective.

In Figure 4, the oblique rays of the Galilean system Figure 2, arerepresented for comparison with Figures 5 and 6 in order to indicate howthe angular field may be made equal to that of the large objective limb.In Figure 4, i, 2, 3 is the objective of the Galilean system; 5, t isthe portion of the negative lens through which the oblique rays pass; 3,5 and 2, 6 are the oblique rays within the limb, while 5, It and 6, iiiare the parallel rays entering the eye which may be most convenientlysituated at the position Hi.

In Figure 5 the objective has been reduced to half the size and itsfocal length correspondingly reduced, with the result that the obliquerays From this diagram it W111 be seen that the semi 4 2, 6 in bothfigures are parallel to one another and the angular fields equal.

In Figure 6 the dioptric system is of the terrestrial telescope type inwhich the objective is represented by I, 2, 3 its focal plane being atthe position 22, 23. An image of this focal plane is transferred to theposition 26, 2! by means of the projector lens 24. The eyepiece 28, 29views the field 26, 21. By suitable adjustment of the field diameter 22,23, the angular field may be made equal to that of the. larger objectivelimb.

Figure 7 represents the equal diameter objectives 42 and 43 customarilyused in a Galilean binocular. Their diameter is determined by theseparation of the centres 44 and 45 equal to the interocular distance ofthe observer. The small space between the objectives is allowed for thethickness of the objective holders. In a Galilean glass there is,therefore, a limit to the objective diameter and therefore to theillumination and night visibility.

In Figure 8, 46 represents the small objective and ll the largeobjective of a binocular constructed in accordance with this invention,separation of the centres 43, 45 being equal to the interoculardistance. Owing to the smallness of the daylight aperture at 46 thediameter of the daylight aperture at 4'! is much increased beyond whathas hitherto been possible in a Galilean glass.

Figure 9 represents a binocular having both limbs of the Galilean type,the limb having a large objective and the other limb 32 a smallobjective. Both limbs are connected together in the usual way by thearms 35, and 36. In this particular example the focussing device is of awell known type, the eyepieces 3| and 32 being carried upon an arm 48which can be movedin or out to suit the focussing by means of thefocussing head 49.

Figure 10 is another arrangement similar to Figure 9 and in which thesame references indicate like parts, but in this case the smaller limb32 comprising a terrestrial optical system, the objectives being more orless in the same plane instead of one behind the other as in Figure 9.

Figure 11 represents a binocular constructed in accordance with thisinvention having a limb 30 of the Galilean type suitable for anobjective whose diameter is greater than that of the interoculardistance. The other limb 32 is of the prismatic type having an objective3'! substantially smaller than the objective of the larger limb andhaving erecting prisms contained within the prism box 34, the fieldbeing viewed by the eyepiece 33. The limbs may be connected by the armsand 36. The magnifying powers and angular fields of the two binocularlimbs are equal.

Figure 12 is a front view (inverted) of Figure 11 showing the eyepiece3i of the larger limb and 33 of the smaller with the connecting arm 35.

Figure 13 is another arrangement of limbs in accordance with thisinvention, both limbs being of the prismatic type, one (33) having alarge objective, the other (32) a small objective, with the angularfields in both cases equal. The prisms of the respective sets arecontained in the boxes fi l and 42. In this particular example the limbsare hinged at the joints 50 and 4| the connecting arms being 35, 36, 38and 39.

Although the daylight apertures at 46 and 4'! (Figure 8) are showncircular they may instead be of some other form, for examplerectangular.

'I claim:

1. A binocular stereoscopic observation instrument for increasing theapparent illumination having two side-by=side optical limbs relativelypositioned for two-eyed viewing by an observer and each including anoptical telescope system with an objective lens and an eyepiece lens;the diameters of the objective lens and-of the light entry aperturethereto of one limb being substantially equal but radically larger thanthese diameters of the other limb, and including means for producingthesame angular field of view in the optical system of each limb wherebythe total objective light entry area to the interior of the instrumentis greater than in the case where the objective lenses are of equalsize.

2. A binocular stereoscopic observation instrument for increasing theapparent illumination having two side-by-side optical limbs relativelypositioned for two-eyed viewing by an observer and each including anoptical telescope system with an objective lens and an eyepiece lens;the diameters of the objective'lens and of the light entry aperturethereto of one limb being substantially. equal but radically larger thanthese diameters of the other limb, and including means for producingthesame angular field of view in the optical-systemof each limb andpresenting at the two eyepiece lenses, aligned and equally magnifiedsimilar views of a common distant object on which the instrument isiocussed by the observer whereby the total objective light entry area tothe interior of the instrument is greater than in the case where theobjective lenses are of equal size.

3. A binocular stereoscopic observation instrument comprising a firstand'second optical limb of the Galilean type arranged side-by-side withtheir. longitudinal axes spaced apart by the limiting interoculardistance and eachIincluding an optical telescope system having acircular objective lens'and'an eyepiece lens respectively locatedadjacent the opposed ends of the limb, the objective lens of the firstlimb being of radius radically greater than half the limitinginterocular distance, and the objective lens of the second limb thefirst limb and less structural clearance,

whereby the total objective light entry area to the interior of theinstrument is greater than in the case, where the objective lenses areof equal size, the focal length of the smaller objective lens being ofcorrespondingly smaller length than that of the larger objective lensand said limbs being of such length as is necessary to provide equalangular fields of view, the optical systems of the two limbs presentingat the two eyepiece lenses, for transmission to the brain of theobserver to be combined therein, aligned and equally magnifled similarviews of images of a common distant object on'which the instrument .isfocussed bythe observer.

4. A binocular stereoscopic observation instrument as claimed in claim3, in which the-first limb is radically greater in lateral dimensionthan the second limb in correspondence with the diametral sizes of theobjective lenses carried by the limbs.

5. A binocular comprising two side-by-side optical limbs, one of theGalilean type and the other of'the terrestrial prismless type,inter-related'for simultaneous two-eyed viewing by an observer and eachincluding an optical telescope system having a circular objective lensand an eyepiece lens, the diameters of the objective lensand-the lightentry aperture of each limb being substantially equal, the diameter ofthe objective lens in the terrestrial typelimb being radically greaterthan that of the other limb and the optical systems of the two limbspresenting at the two eye'- piece lenses for transmission to the brainof the observer to. be combined therein, aligned an equally magnifiedview of the images, of a common distant object on which the instrumentis focussed by the observer, and means for producing the same angularfield of view in the optical system of each limb whereby the totalobjective light entry area to the interior of the instrument is greaterthan in the case where the objective lenses are of equal size.

6. A binocular as claimed in claim 5, in which the diameter of thefield'in the focal plane of the terrestrial prismless type limb isadjusted, to provide an angular field equal to that of the other limb.

7. A binocular stereoscopic. observation instrument as claimed in claim1, in which one limb is of the Galilean type and the other 01 theprismatic type.

8. A binocular stereoscopic observation instrument as claimed in claim2, in which one limb is of theGalileantype and the other of theprismatic type.

JAMES WEIR FRENCH.

References Cited in the file of this patent.

UNITED STATES PATENTS Number Name Date 569,528 Toussaint Oct. 13, 1896804,996 Anthony Nov. 21, 1905 841,262 Martin Jan. 15, 1907 1,714,849Daponte May 28, 1929 1,891,641 Habel Dec. 20, 1932 2,166,102 Wild July18, 1939 2,406,190 Burdick Aug. 20, 1946 FOREIGN PATENTS Number CountryDate 10,493 Great Britain of 1908 20,390 Great Britain of' 1908 498,167France Oct. 8, 1919 527,514 Germany May 6, 1932

